Industrial power users are rapidly becoming aware of the importance of monitoring distributed power networks. Proper monitoring can provide tangible benefits with respect to equipment operation and maintenance; therefore, significant return on investment. More specifically, these benefits include savings in terms of equipment energy cost and maintenance costs, better equipment utilization, and increased system reliability.
Electric utility applications have ranged from supervisory control and data acquisition (SCADA) systems, primarily concerned with remote operations, to distribution automation, which focuses on operating efficiency. Certain utility applications have included devices mounted on power lines for sensing operating parameters of an associated power conductor. For example, U.S. Pat. Nos. 5,224,054 and 5,233,538 describe a circuit monitoring system for a distributed power network. The system includes a plurality of metering units and a control station, which is coupled to each of the metering units via a multi-drop communications link. Each of the metering units is disposed adjacent to an associated one of the branches in the network for sensing power parameters in the branches and for generating and transmitting data representing the power parameters to the control station. The control station is used for generating monitoring commands to each of the metering units to provide the system with full system control and evaluation capability.
In order to expand the capabilities of the metering units and keep the metering units up-to-date with the latest system enhancements, downloadable firmware permits a user to update existing main functionality firmware in the metering units. One drawback of existing metering units is that the metering units do not support multi-drop or network communications protocol or broadcast download capability. Therefore, a metering unit cannot be updated from the control station, but rather must be updated by first disconnecting the metering unit from the multi-drop communications link to remove the metering unit from service and by then connecting a portable personal computer containing the firmware updates to the metering unit using a separate communications link.
Another drawback of existing metering units is that they employ a conventional flash EEPROM to store the main functionality firmware to be updated. Since the entire flash EEPROM must be erased while updating the EEPROM, any essential (i.e., non-erasable) firmware must be stored in a separate integrated circuit memory so that it is not erased during the updates. This additional memory provides an added production cost. Examples of essential firmware, which must maintain integrity at all times, include the section of firmware executed on unit reset (i.e., boot code) and the section of firmware supporting the communications protocol.
A need therefore exists for a metering unit which overcomes the above-noted drawback associated with existing metering units.